1. Field of the Invention
The present invention relates to an image forming apparatus capable of performing another image formation job by interrupting a current image formation job and, after completion of that image formation job, resuming the previous image formation job.
2. Description of the Related Art
In recent years, with advances in network technology and the technology of digitally processing image data, it has become popular to integrate various apparatuses such as a copying machine, a printer, a facsimile machine, and a scanner, into a single multifunction apparatus capable of providing various functions. In such a multifunction apparatus, a large number of processing requests are often issued at the same time by users via an operation control unit of the apparatus or via a network. To deal with such a situation, the multifunction apparatus is capable of accepting a plurality of requests for performing various functions and also capable of performing a plurality of processes in response to the plurality of processing requests, both individually or in parallel in an efficient manner.
However, even in a case in which a plurality of requests including a similar process are issued at the same time, only one request is processed and the other requests have to wait for completion of the process being currently performed. For example, when a copy request and a print request are issued at the same time, one of the two requests has to wait for completion of the process of printing on sheets performed in response to the other request. If the process being currently performed needs a long time to complete, the waiting process cannot be started until the current process has been completed. Thus, it takes a long time to complete the waiting process even if the waiting process itself needs a short time.
To avoid the above problem, it is known to interrupt a process being currently performed and perform another process as an interrupt image formation job. In this method, priority is given to each processing request, and if a processing request having high priority is issued in the middle of performing a process having lower priority, the current process is interrupted at a proper time and the high-priority process is performed. After completion of the high-priority process, the interrupted process is resumed.
Before starting the interrupt image formation job, data indicating the setting of the current image formation job (interrupted image formation job) is saved. When the interrupt image formation job is completed, the setting of the previous job (interrupted image formation job) is automatically recovered and the previous job is resumed correctly. However, a change can occur in the amount of an expendable supply relative to the amount before the interrupt because the interrupt image formation job consumes the expendable supply.
In a case in which the expendable supply consumed during the interrupt image formation job is a supply such as sheets or toner which is not of a special type, the same type of supply remains in a storage unit. That is, in this case, no change occurs in the type of the supply during the interrupt job, and thus there is no problem as along as a sufficient amount of supply remains. However, if ordered sheets whose order is important, such as tab sheets whose tab position vary from one sheet to another, are consumed during an interrupt image formation job, the interrupted image formation job will encounter a difference in the order of sheets when it is resumed, and thus the interrupted image formation job will resume in a manner different from an intended manner.